It is advantageous for an earthmoving implement of an earthmoving machine such as a track/wheel bulldozer to be operated in a manner that results in the greatest productivity. Often manual control of an earthmoving implement, such as a bulldozer blade, is inefficient, particularly over a period of time as the operator tires.
Maximum productivity can be achieved by maximizing the "draft power" of the earthmoving machine. Draft power is the rate of actual useful work being done in moving the soil and is defined as the product of the draft force of the earthmoving implement and the ground speed of the earthmoving machine.
In the example of a bulldozer, draft force is the force on the blade. Maximum draft power is reached when the bulldozer is moving at optimum ground speed commensurate with draft force. For typical bulldozer operation, a ground speed of 1.6 mph allows for optimum power and efficiency. Operators do not have direct ground, speed feedback and they cannot see the load on the blade. Accordingly, operators often control the bulldozer on their sense of slip and engine speed. The use of slip as a feedback mechanism is inefficient because slippage does not occur until productivity hats already been lost. Operators that rely on their sense of slip feedback tend to run the bulldozer at a rate slower than that needed to achieve maximum power and efficiency. On the other hand, operators that rely on engine speed tend to run the bulldozer at a rate faster than that needed to achieve maximum power and efficiency.
Difficulties are often encountered in the control of the earthmoving implement when different ground profiles are encountered by the earthmoving machine. The earthmoving implement's position must be changed so that it won't dump its accumulated load nor cut to deeply, and still create a smooth cut. In addition, to maintain maximum efficiency, it is essential that the operator or the control system be able to differentiate between different ground profiles such as humps, rocks, and grade change.
Control systems have been developed that provide information for controlling the blade during various working conditions. However, the prior automatic control systems do not adequately control the blade position to achieve maximum efficiency in the variety of ground profiles encountered in operation. For example U.S. Pat. No. 4,630,685 by Huck et al. (the '685 Patent), discloses an apparatus for controlling an earthmoving implement using angular velocity. The '685 Patent is a relatively basic system in which ground speed and angular velocity directly control the actuator without an intervening loop on implement position. The lack an implement position control loop and the reliance on angular velocity results in lower operating efficiency when the earthmoving machine encounters varying ground profiles.
The present invention is directed to overcoming one or more of the problems as set forth above.